The present invention relates to carbon-containing refractories and in particular magnesite-carbon refractory brick suitable for use in metal processing equipment, especially basic oxygen furnaces (BOF) and other metallurgical vessels wherein the principal mode of wear of the refractory brick lining is slag attack and where high hot strength and high slag resistance of refractory linings are required.
Carbon-containing basic refractory brick have been used in basic oxygen furnaces and other metal processing equipment for many years. In the United States, for example, pitch bonded and burned pitch impregnated magnesite brick have been used since the early 1960's. In other areas of the world, different practices have been used. For instance, pitch bonded and burned pitch impregnated dolomite brick have been used in Europe. In Japan, burned pitch impregnated basic brick with relatively high levels of lime (e.g. 30% CaO and 70% MgO) have been used.
In the late 1970's and early 1980's, a major advance in the technology of refractories for BOF and other vessels was realized with the introduction of magnesite-carbon brick. Unlike the brick that had traditionally been used, these brick contained graphite. Flake graphite was used most often, although in some cases Sri Lankan vein graphite was employed. These magnesite-carbon brick generally had high carbon contents ranging from about 8 to 30%, while the traditional brick contained a maximum of 5% carbon as a rule.
The term "magnesite-carbon brick" as generally used in this industry, and as used herein, refers to brick that contain graphite in combination with deadburned magnesite or magnesia, with the brick containing in excess of 8% by weight carbon.
While use of the magnesite-carbon brick in basic oxygen furnaces and other metal processing equipment did result in longer times between relines, it was perceived in early trials that the performance of these brick could be improved by increasing their hot strength and oxidation resistance. As a result, magnesite-carbon brick that contained powdered metals were developed. These brick have been described in U.S. Pat. No. 4,306,030. The metals used in these brick were aluminum, silicon, and magnesium. The metals increased oxidation resistance by lowering the permeability of the brick and by consuming oxygen that would otherwise have oxidized carbon.
However, the addition of a metal such as aluminum, silicon, and magnesium can have undesirable effects as is set forth in parent U.S. Application Serial No. 274,387 and the product thereof is a "metal-free" mix; i.e. one that does not contain any such metal in any amount to have any effect.
While the "metal-free" brick of such parent patent application represents a significant improvement in refractory technology, a further increase in the wear resistance and strength thereof is desirable.
It is also known as set forth in U. S. Pat. No. 4,431,745 that adding amounts of metal less than 0.5 wt.% does not produce the desired effects of increasing wear resistance and oxidation resistance. Also, as is shown in this patent the use of high levels of metal addition results in decreasing corrosion resistance. It is also known that metal addition can have other negative effects such as the fluxing action caused by oxidized aluminum, increased porosity and porous textures caused by volatilized magnesium, and the loss of carbon from the brick due to the reduction of silica formed from oxidized silicon in the presence of carbon.